1. Field of the Invention
The present invention relates to a dual thyristor, that is, to a component, the features of which can be induced from those of a conventional thyristor by applying the duality principle to the current and voltage behaviors and to the control modes.
2. Discussion of the Related Art
FIG. 1A shows a conventional thyristor Th including an anode A, a cathode K, and cathode and anode gates GK and GA.
The characteristic curve of a thyristor is illustrated in FIG. 1B. This component exhibits the following features:
it is normally off, PA1 it is a one-way component for the current, that is, it is likely to let through a positive current I.sub.A but blocks a negative current, PA1 it is bidirectional for the voltage, that is, it is likely to withstand positive or negative voltages in the off state, PA1 it can be triggered by a current pulse applied to its gate when the voltage thereacross is positive; this is illustrated in FIG. 1B by curve 10, that is, when a gate current is applied thereto, it turns on by break over, and its characteristic becomes that indicated by curve 11, PA1 it is self-triggering when the voltage thereacross exceeds a value VBO in the absence of a gate current, PA1 it spontaneously turns off when the current flowing therethrough becomes low (lower than a hold current value I.sub.H). PA1 it is normally on, PA1 it is bidirectional for the current, that is, a positive current as well as a negative current can flow therethrough (the flowing of a negative current is ensured by diode D illustrated in FIG. 2A), PA1 it is a one-way component for the voltage, that is, it is likely to withstand positive voltages only, in the off state, due to the presence of diode D, PA1 it can be turned off by a voltage pulse applied to the gate, that is, if, while the operating point is on curve 20, a control voltage is applied, the operating characteristic will become that designated with reference 21, PA1 it has a self turn-off characteristic, that is, if the current flowing therethrough exceeds a value I.sub.BO, it turns off by itself, PA1 it spontaneously triggers at voltage zero crossing, that is, it turns on if, while in the off state, the voltage thereacross drops below a threshold voltage V.sub.H.
The symbol of a dual thyristor is illustrated in FIG. 2A. This dual thyristor has current-voltage characteristics which are dual with respect to those of a conventional thyristor, as is shown in FIG. 2B:
In other words, while a thyristor forms a normally off one-way component for the current, which can be triggered by a control current or be self-triggering beyond a given voltage threshold, a dual thyristor forms a normally on switch which can be turned off by a control voltage or be self-locking beyond a given voltage threshold.
In prior art, the implementation of a system having the function of a dual thyristor has been performed by associating a specific control circuit with a switching component. This solution has two disadvantages. The first one is that it is always difficult to monolithically associate control circuits with a power component. The second one is that it is necessary to provide for the control circuit a bulky auxiliary power supply, which is costly and possibly sensitive to surrounding disturbances. A simplified dual thyristor not controllable by pulses is described in EPE'95: 6TH European Conference on Power Electronics and Application, Seville, Sep. 19-21, 1995, vol. 1, Sep. 19, 1995, P. 1.637 to 1.642, X P OOO537596, J-L Sanchez et al.